Fluorine-containing melt-processable resins such as tetrafluoroethylene-perfluoroalkyl vinyl ether are excellent in chemical resistance, weatherability, heat resistance, non-stickiness and the like, and further are melt-processable. Therefore, the resins are used for enhancing functions such as corrosion resistance, non-stickiness and low abrasion by coating, for example, heat resistance substrates such as iron, aluminium and stainless steel.
Conventionally, as for such a use, there are paints of organic solvent type prepared by dissolving fluorine-containing melt-processable resins in organic solvents, and aqueous dispersion paints prepared by dispersing fluorine-containing melt-processable resins in water (JP-B-10896/1982).
The aqueous dispersion compositions are safe and easy to handle, and coatings thereof are formed by applying onto a primer layer of a substrate with brushing or air spraying, and then drying and sintering.
Since resin particles in the conventional aqueous dispersion paints are small in size, however, when increasing a thickness of one application, cracks occur on the resulting coating. Therefore, a coating obtainable by one application has a thickness of at most 50 .mu.m. In order to make the coating thicker even if the number of applications increases, cracks also occur when the thickness is large. Accordingly, a thickness of the coating prepared by recoating method cannot be beyond 1 mm.
Aqueous dispersion paints containing binders disclosed in JP-A-10896/1982 cannot be used in recoating method.
An object of the present invention is to provide aqueous dispersion compositions of fluorine-containing melt-processable resins which can increase a thickness of coating per one application and can give thicker coatings having no crack.